.NET Framework Class Library Rule Enumeration
Namespace:
System.Data
Assembly:
System.Data (in System.Data.dll)
Syntax
Remarks
The Rule values are set to the UpdateRule and the DeleteRule properties of a ForeignKeyConstraint object found in a DataTable object's ConstraintCollection. The Rule values determine the action that occurs when a value in a column is either deleted or updated. Of the two, deleting a value is the more critical and demanding of attention when setting a rule. In the case where a value is deleted, Cascade specifies that all rows containing that value are also deleted. SetNull specifies that values in all child columns are set to null values. SetDefault specifies that all child columns be set to the default value for the column. None specifies that no action will occur, but exceptions are generated. In the case where a value is updated, Cascade specifies that all child columns are likewise updated with the new value. SetNull specifies that all child columns be set to null values. SetDefault specifies that all child column values be set to the default value. None specifies that no action be taken, but exceptions are generated. Constraints on a DataSet are not enforced unless the EnforceConstraints property is true. When the AcceptChanges method is called, the AcceptRejectRule further determines what action occurs.
Examples
' The next line goes into the Declarations section of the module:
' SuppliersProducts is a class derived from DataSet.
Private suppliersProducts As SuppliersProducts
Private Sub CreateConstraint()
' Declare parent column and child column variables.
Dim parentColumn As DataColumn
Dim childColumn As DataColumn
Dim fkeyConstraint As ForeignKeyConstraint
' Set parent and child column variables.
parentColumn = suppliersProducts.Tables("Suppliers").Columns("SupplierID")
childColumn = suppliersProducts.Tables("Products").Columns("SupplierID")
fkeyConstraint = New ForeignKeyConstraint( _
"SupplierFKConstraint", parentColumn, childColumn)
' Set null values when a value is deleted.
fkeyConstraint.DeleteRule = Rule.SetNull
fkeyConstraint.UpdateRule = Rule.Cascade
fkeyConstraint.AcceptRejectRule = AcceptRejectRule.Cascade
' Add the constraint, and set EnforceConstraints to true.
suppliersProducts.Tables("Products").Constraints.Add(fkeyConstraint)
suppliersProducts.EnforceConstraints = True
End Sub
Version Information
.NET FrameworkSupported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0 .NET Framework Client ProfileSupported in: 4, 3.5 SP1
Platforms
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role not supported), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
See Also
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Biblioteca de clases de .NET Framework Rule (Enumeración)
Espacio de nombres:
System.Data
Ensamblado:
System.Data (en System.Data.dll)
Sintaxis
Comentarios
Los valores de Rule se establecen en las propiedades UpdateRule y DeleteRule de un objeto ForeignKeyConstraint encontrado en un ConstraintCollection de un objeto DataTable. Los valores de Rule determinan la acción que se produce cuando se elimina o actualiza un valor de una columna. De estas dos posibilidades, la eliminación de un valor es la más importante y la que requiere una mayor atención al establecer una regla. En caso de que se elimine un valor, Cascade especifica que se eliminen también todas las filas que contengan ese valor. SetNull especifica que los valores de todas las columnas secundarias se establezcan en valores nulos. SetDefault especifica que todas las columnas secundarias se establezcan en el valor predeterminado de la columna. None especifica que no se realice ninguna acción, pero que se generen excepciones. En caso de que se actualice un valor, Cascade especifica que se actualicen también todas las columnas secundarias con el nuevo valor. SetNull especifica que todas las columnas secundarias se establezcan en valores nulos. SetDefault especifica que los valores de todas las columnas secundarias se establezcan en el valor predeterminado. None especifica que no se realice ninguna acción, pero que se generen excepciones. Las restricciones de un DataSet no se fuerzan a menos que la propiedad EnforceConstraints sea true. Cuando se llama al método AcceptChanges, AcceptRejectRule se determina exactamente qué acción se va a producir.
Ejemplos
' The next line goes into the Declarations section of the module:
' SuppliersProducts is a class derived from DataSet.
Private suppliersProducts As SuppliersProducts
Private Sub CreateConstraint()
' Declare parent column and child column variables.
Dim parentColumn As DataColumn
Dim childColumn As DataColumn
Dim fkeyConstraint As ForeignKeyConstraint
' Set parent and child column variables.
parentColumn = suppliersProducts.Tables("Suppliers").Columns("SupplierID")
childColumn = suppliersProducts.Tables("Products").Columns("SupplierID")
fkeyConstraint = New ForeignKeyConstraint( _
"SupplierFKConstraint", parentColumn, childColumn)
' Set null values when a value is deleted.
fkeyConstraint.DeleteRule = Rule.SetNull
fkeyConstraint.UpdateRule = Rule.Cascade
fkeyConstraint.AcceptRejectRule = AcceptRejectRule.Cascade
' Add the constraint, and set EnforceConstraints to true.
suppliersProducts.Tables("Products").Constraints.Add(fkeyConstraint)
suppliersProducts.EnforceConstraints = True
End Sub
Información de versión
.NET FrameworkCompatible con: 4, 3.5, 3.0, 2.0, 1.1, 1.0 .NET Framework Client ProfileCompatible con: 4, 3.5 SP1
Plataformas
Windows 7, Windows Vista SP1 o posterior, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (no se admite Server Core), Windows Server 2008 R2 (se admite Server Core con SP1 o posterior), Windows Server 2003 SP2
.NET Framework no admite todas las versiones de todas las plataformas. Para obtener una lista de las versiones compatibles, vea Requisitos de sistema de .NET Framework.
Vea también
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